The novel was original the author had his own website. But i forgot the name and the website wasn't bookmarked. I had dropped it because last time I saw it, it was hardly updated been like 3 months at that time. Summary: MC have system he is harem seeking male protagonist. The book had incest element which was his sister. The world is modern world but have magic element to it. The magic element more like awakening which you have limited power you get etc. The system have love meter, which will make any girl that reach 100% will be loyal will not be able to betray him. I think he get point and can buy from system aprodasic and sleeping pill. he got caught by his sister. MC goal was to create harem for himself and protect his harem. Their parent were absent was mentioned in the novel but had yet to make appearance.
Look up harem, sex, system tags on scribblehub its somewhere in first couple pages of search there. Sorry, can't recall the name either, Sex beast or hentai system or something.